\documentclass[12pt]{article}
%\documentclass[dvipdfm]{beamer}  %dvipdfm选项是关键,否则编译统统通不过

\usepackage{fontspec,xltxtra,xunicode}
\setmainfont[Mapping=tex-text]{宋体}

\begin{document}

\newfontfamily{\K}{Kai}
\newfontfamily{\F}[Scale=1.9]{FangSong}
\newfontfamily{\H}[Scale=1.85]{SimHei}

%\frame{\frametitle{基础理论}

宋体\\

{\K 楷体}

\end{document}  